Copycat Criminals
The recent wave of bank robberies seems to me typical of the relaxed but opportunistic Portuguese attitudes.
In general, the Portuguese are not physically violent; though very prone to verbal abuse. We can even see this in their approach to bank robbing - weapons are carried but never used. The impersonal institution loses a small amount of cash while customers are rarely victims. This is hardly "violent" crime, as seen in other countries.
Why this sudden wave of crime? Because the media has explained clearly and repeatedly that the probability of being caught is practically zero. The crimes last only a few minutes and the police are unlikely to get there in time. It's similar to the chronic disregard for traffic law, which has fallen significantly as the chances of being caught increase.
I don't think this recent increase is due to the recession, just opportunism, a fad that will wear off soon.